Genomics' Contribution to EVA Research and Beyond

Genomics' Contribution to EVA Research and Beyond

Scientists have since used equine genome information to study reproduction, muscle physiology, immunology, diseases, performance, and coat colors in horses.

Photo: iStock

In the past two decades the field of equine genomics has exploded, leading to the discovery of genetic variants for coat colors, gene associations with athletic ability, and gene mutations responsible for a variety of health conditions and diseases.

Starting in 1995, Ernie Bailey, PhD, an equine geneticist and professor at the University of Kentucky's (UK) Gluck Equine Research Center, coordinated an international effort to create a gene map for horses; this ultimately led to sequencing the horse genome in 2006. The effort involved more than 200 scientists from 30 institutions and created valuable research tools to address equine health problems that had not yielded to earlier technologies.

At the 13th Mary Passenger Memorial Lecture on Equine Medicine and Surgery, held Oct. 10, Bailey—one of this year's Equine Research Hall of Fame inductees—spoke about advances in equine genomics and their contribution to equine viral arteritis (EVA) studies. He began with a brief history of genome sequencing.

A key event occurred in 2003 when geneticists completed the human genome. They discovered that humans have 20,000 genes and that only 2% of DNA encodes the proteins. This led to the question, "What is the role of the other 98% of our DNA”?

 

Because the genome's size and organization are consistent across all mammals, scientists began sequencing certain animals to answer that question and better understand the human genome. One of those mammals was the horse.

Scientists have since used equine genome information to study reproduction, muscle physiology, immunology, diseases, performance, and coat colors in horses. Bailey, with his students and colleagues, published studies on genes controlling the immune response, coat color genes, the genetics of swayback in Saddlebreds, and dwarfism in Miniature Horses. Recently, Bailey said the team at UK has made genetic discoveries related to equine arteritis virus (EAV) infections in horses.

EVA is a contagious infectious disease that can cause respiratory disease, abortion in mares, and a persistent carrier state in stallions. Affected stallions become natural sources of equine arteritis virus (EAV) and continue to shed the virus in their semen.

In 2011 Yun Young Go, DVM, MSc, PhD, a former graduate student in the laboratory of Udeni Balasuriya, BVSc, PhD, professor of virology at the UK Gluck Center, found that EAV infected CD3+T lymphocytes (a subpopulation of white blood cells) in some horses but not others. She, Balasuriya, Bailey, and colleagues evaluated 16 stallions that were susceptible to EVA infectivity and 21 that were resistant and discovered that many differences between these two groups occurred on chromosome 11 (ECA11). In other words, somewhere on ECA11 are the genes responsible for EVA severity and development of the carrier state.

They subsequently discovered a strong association between stallions that were shedders and those that had the susceptibility gene. The next step was to sequence this gene in species related to the horse (i.e., rhinos, tapir, zebras, donkeys, etc.) to determined the origin of sequences for resistance and susceptibility. They found that:

  • Donkeys and zebras had the same allele (form of the gene) as susceptible horses;
  • EAV susceptibility might be ancestral among Equidae; and
  • EAV resistance might be newly evolved in the horse.

This work identified new targets for therapeutic treatment of EVA. "In the future we can identify and use susceptible horses when we are investigating methods to control EAV infections," Bailey concluded.

Alexandra Beckstett is the managing editor of The Horse: Your Guide to Equine Health Care.


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About the Author

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

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